AngularJS 1.5 component get parent ngModel

Question

I can't change ngModel defined in $ctrl. It looks like this: 1. I have next code, defining component in index.html:

<div ng-controller="appControllerData">
    ...
    <div ng-controller="appControllerData as datactrl">
        <filter-userstat userstat="'isPolicyHolder'"></filter-userstat>
    </div>
    ...
</div>

2. I have component file (filter_userstat.html):

<div>
    <input type="checkbox" value="true" ng-model="$ctrl.usersFilter[$ctrl.userstat]"> Some value
</div>

3. I have a component (filter_userstat.js):

appModule.component('filterUserstat', {
    templateUrl: 'filter_userstat.html',
    controller: filterUserstatController,
    bindings: {
        userstat: '<'
        // , usersFilter: '<' // I tried everything without any success 
    }
});

function filterUserstatController(){
    // ...
}

4. I have usersFilter in my controller:

   this.usersFilter = $scope.usersFilter = { .... };

When I click on the checkbox it seems doesn't affect on the parent's model, whatever I did. However if I relocate this code in the index.html as was set before, everything works just perfect. So as I can conclude it is needed to link the parent ngModel with the one in the component. But I can't find out the way yet. Has anybody suggestion?